Learn Kotlin by Example

Introduction⌗

Functions⌗

fun aFunction(arg1: Arg1Type, optionalArg: OptionalArgType = defaultVal): ReturnType {
// ...
}

fun printStuff(stuff: String, prefix: String = "Info") {
    print("[$prefix] $stuff")
}

fun main() {
    // Many valid ways to call printStuff
    print("thing")
    print("thing", "hello")
    print(stuff = "thing", prefix = "hello")
    print(prefix = "hello", stuff = "thing")
}

Infix Functions: `infix`⌗

Member and extension functions with a single parameter can be turned into infix functions (calling it doesn’t require a dot or parentheses)

Almost in a way making your own keywords? Probably how Boolean or is just ‘or’

infix fun Int.times(str: String) = str.repeat(this)
println(2 times "Bye ")

Bye Bye

Operator Overloading ⌗

In an addition to infix functions, using the operator keyword with some special names will overload an operator symbol

operator fun Vector.plus(v2: Vector) = Vector(this.x + v2.x, this.y + v2.y)
println(aVector + anotherVector)

Varargs⌗

A funky kind of inline array? Come back to this.

The mechanism by which listOf() works, I think

Class Declarations⌗

In Kotlin, both the header and the body are optional, since the compiler can build the constructor and appropriate getters/setters for you

// All valid class declarations

class Customer
// a default constructor is inferred

class Contact(val id: Int, var email: String)
// builds a constructor

fun main() {
    val contact = Contact(1, "[email protected]")
    println(contact.email)
    contact.email = "[email protected]"
    println(contact.email)
}

[email protected] [email protected]

Note: `new` keyword doesn’t exist in Kotlin⌗

Inheritance⌗

Classes and functions are final by default in Kotlin. If you want one to be able to be overriden, mark it with the open keyword.

open class Dog {
    open fun sayHello() {
        println("woof")
    }
}

class Yorkshire : Dog() {
    override fun sayHello() {
        println("yip")
    }
}

fun main() {
    val dog: Dog = Yorkshire()
}

Control Flow⌗

To be continued…

Kotlin Basics